In film vapor deposition processes, it is known to load a furnace tube under vacuum by employing a transfer mechanism for pushing a boat containing a number of semiconductor wafers to be coated with film into the furnace, and upon completion of the deposition of film on the wafers, the boat is pulled out of the furnace to retrieve the coated wafers. This situation is significantly more complicated if the furnace tube and the boat transfer mechanism are under high vacuum. In this case the transfer mechanism cannot be easily adjusted during operation because of the restriction of movement imposed by the required vacuum feedthrough.
The boat transfer arm has a length of several feet, e.g. four, to accommodate the extent of travel required upon inserting and removing the boat with respect to the furnace. Typically, the transfer arm is coupled to the wafer boat by an "L" shaped terminal arm portion, which fits into a hole in a horizontal boat plate extending from an end of the boat. The boat is transported in and out of the furnace by pushing and pulling on the transfer arm manually. However, displacement of the transfer arm from a horizontal plane could produce force vectors perpendicular to the length of the boat, subjecting the boat to tipping or jamming. Even if the transfer arm is maintained in the horizontal plane by a support, the arm would still be subjected to sagging due to the effect of gravity on the elongated and now cantilevered four foot arm. Hence, if this sagging of the long transfer arm is not somehow dealt with, the "L" shaped terminal arm portion can still push down on the boat to cause detrimental tipping and possible jamming of the boat with respect to the furnace supporting floor. Thus, a simple and reliable boat transfer mechanism is desired for eliminating this problem.